Motor Car Battery -> 12V Supply

Hi

I have a DC-DC convertor (B1205LS/D-1W) that takes 12V (10.8V -> 12.3V) and outputs 5V.
I would like to use this to power my ciruit from my vehicle battery.

The car battery Can go as high as 15V (I`ve heard) and while charging is roughly 14V and normaly 12V.

Can someone suggest a simple method to ensure/limit the Voltage to 12V?

I looked into a 12V zener but I belive for this to work adaquatly you need to have a few volts above 12 always and the battery will sometimes be 12V only.

Any ideas/suggestions will be appreciated.

Are you asking how to reduce the battery voltage so that it doesn't damage the switcher? The car battery will get to ~14.5V with the engine running/alternator charging. The data sheet I looked said it will take up to 13.3V, so put two silicon diodes in series, cathodes toward the switcher, in the positive lead. Since the switcher is ~85% effecient, the current drawn by the switcher should be 1/(5*0.85)*(5/12) = 0.1A so 1N400x diodes will work fine.